The U.S. Pat. Nos. 4,473,732; 4,560,851 and 4,847,746 disclose the applications of a high frequency switching circuit to the electromagnetic induction heating device. Such applications generally involve various high frequency switching circuits which are designed differently. The U.S. patent Ser. No. 07/858283, the German Patent G9204812.9 and the Taiwanese Patent 85167 disclose a novel dual push-pull induction heating circuit. The circuits mentioned above are aimed at regulating one or two power transistors to act on the ON-OFF switching so as to control the induction coil to output the high frequency switching circuit. In other words, the power transistor must bear a considerably high transient collect voltage and a considerably high transient collect current. In addition, the switching power loss of the power transistor is great. As a result, a power transistor having a greater collect loss specification must be used in the circuit. A greater switching power loss is often responsible for the high rate of the breakdown of the power transistor.
The power transistor having a greater collect loss specification is generally expensive and bulky. In addition, such a power transistor as described above generates a considerable heat, which must be radiated by a heat-radiating means, thereby undermining the efficiency of the electromagnetic heating device. The switching power loss of the power transistor can be reduced by lessening the value of resistance of the power transistor gate at the risk of causing a voltage surge in the drive circuit.